Final answer:
To find the expression 2C - D, substitute the given expressions for C and D into the expression. Expanding and simplifying gives -y² + 2y + 19.
Step-by-step explanation:
To find an expression that equals 2C - D, we substitute the given expressions for C and D into the expression. Given that C = y + 5 and D = y² - 9, we have:
2C - D = 2(y + 5) - (y² - 9).
Expanding and simplifying the expression gives:
2(y + 5) - (y² - 9) = 2y + 10 - y² + 9 = -y² + 2y + 19.
Therefore, the expression 2C - D, in standard form, is -y² + 2y + 19.
Learn more about Expression simplification